Device for promoting formation of bone material

ABSTRACT

A device for promoting the formation of bone material in the region of the bone structure of a living being by the application of an A.C. signal, including at least two metal electrodes, which can be inserted into the bone, and an A.C. signal source, which has at least two connecting wires. Each of the connecting wires is connected to a corresponding one of the metal electrodes. A locking element is connected to the end of each connecting wire and a corresponding receiving element is disposed on each of the electrodes. By interlocking of the locking element with the corresponding receiving element, the connection between the connecting wire and the corresponding electrode is effected.

United States Patent [191 Kraus 1 Nov. 11, 1975 1 DEVICE FOR PROMOTING FORMATION OF BONE MATERIAL [76] Inventor: Werner Kraus, 31 Bauerstrasse, D-8

[30] Foreign Application Priority Data Mar. 9, 1973 Germany 2311817 [52] US. Cl. l28/82.1; 128/419 F; 339/217 R [51] Int. Cl. A61N l/OO [58] Field of Search l28/82.l, 2.1 E, 2.06 E,

128/419 P, 419 F, 83, 418, 404, 420, 421, 413, 303; 3/1; 339/217 R, 218 R, 91 R [56] References Cited UNlTED STATES PATENTS 3,151.619 10/1964 Sullivan 128/418 X OTHER PUBLICATIONS Electro-Osteograms of Long Bones of Immature Rabbits, Friedenberg et al., J. Dent. Res, June, 1971. Effect of Microamp Electrical Currents on Bone ln Vivo, Nature, Vol. 231, May 1971.

Electrical Current Effects on E. coli Growth Rates, Proceeding of the Soc. for Experimental Photogy & Medicine, Vol. 139, Mar. 1972.

Primary Examiner-Richard A. Gaudet Assistant Exmniner-J. Yasko Attorney, Agent, or Firm-Spencer & Kaye ABSTRACT A device for promoting the formation of bone material in the region of the bone structure of a living being by the application of an AC. signal, including at least two metal electrodes, which can be inserted into the bone, and an AC. signal source, which has at least two connecting wires. Each of the connecting wires is connected to a corresponding one of the metal electrodes. A locking element is connected to the end of each connecting wire and a corresponding receiving element is disposed on each of the electrodes. By interlocking of the locking element with the corresponding receiving element, the connection between the connecting wire and the corresponding electrode is effected.

6 Claims, 8 Drawing Figures ll|||l Patent Nov. 11,1975 Sheet10f3 3,918,440

UQEEGIESP U.S. Patent Nov. 11, 1975 Sheet 2 01 3 3,918,440

DEVICE FOR PROMOTING FORMATION OF BONE MATERIAL BACKGROUND OF THE INVENTION The present invention involves a device. for promoting formation of bone material for assisting in the healing of bone damage by the application of an A.C. signal.

It is known that the healing of bone fractures and the regeneration of bone substance is promoted by lowfrequency electrical alternating currents. German Pat. No. L9 1 8,299, corresponding to my US. patent application Ser. No. 26,809, filed April 9, 1970, now US. Pat. No. 3,745,995 issued July 17, 1973, describes a device including a splint for repositioning and healing of fractured bones, to which an A.C. signal is applied. The device disclosed by my prior application includes a pick-up coil, whose ends are connected to metal electrodes inserted in the region of the bone to be treated. The pick-up coil can have an A.C. signal magnetically induced therein and thus effectively acts as an A.C. signal source.

In many cases, it is not necessary to fix the injured or damaged bone by the use of a separate supporting element, such as a plate or medullary nail, but it is suffrcient to connect the fractured parts together by the use of either bone screws or so-called Kirschner wires.

The Kirschner wires, which can be externally inserted, are strong, thin, metal rods, which are forced through both parts of a broken bone and are then clamped together by two turnbuckles mounted on the ends of the rods projecting from the damaged limb for pressing the fractured parts of the bone together. Where bone screws and Kirschner wires are to be utilized, there is a need for a device operating on the above-mentioned principle of applying an A.C. signal to assist in the formation of bone material, which can be easily utilized, even under difficult conditions, by the physician treating the case.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved device for applying an A.C. signal to a bone structure.

Another object of the present invention is to provide a device in which the wires from the A.C. signal source are securely connected to the electrodes to be inserted into the bone structure.

A further object of the present invention is to provide a device for applying an A.C. signal to a bone structure in which either bone screws or Kirschner wires are utilized as the electrodes to be inserted into the bone structure.

These objectives are carried out in accordance with the present invention in that the metal electrodes and the corresponding connecting wires of the device for applying the A.C. signal are provided with mating lockable connecting elements. The interconnection of these lockable connecting elements provides a firm mechanical and secure electrical connection between the connecting wires and metal electrodes which can be simply i and conveniently made.

nected between the A.C. source and a respective one of the metal electrodes. Each of the connecting wires is provided with a locking element and each of the electrodes is provided with a corresponding receiving element to receive the locking element of the corresponding connecting wire. The connecting wire and the corresponding electrode are connected by the interlocking of the respective locking element and the respective receiving element.

In accordance with one embodiment of the present invention, the metal electrodes are bone screws, each of which has a recess in its head so as to form a receiving element. Each of the connecting wires from the associated A.C. signal source is provided with a locking element which is formed so as to securely fit within the recess in the head of the corresponding bone screw. The locking elements in addition to providing a mechanism for electrically connecting the connecting wires to the bone screw also serve to mechanically connect the A.C. signal source, which is preferably a magnetic pickup coil, to the bone screws.

The recess in the head of the bone screw can preferably be in the form of an hexagonal socket with a widerred portion at its inner end. The locking element associated with the corresponding connecting wire is constructed so that it corresponds to the hexagonal socket. Wires, which are connected to the connecting wire and are constructed so as to effectively act as springs, are arranged on the inserted portion of the locking element so as to be clamped between the locking element and the socket. This locking element is preferably made of a plastic material and has a cap-like shape.

This plastic cap-like locking element is preferably substantially mushroom shaped and has a shank which fits into the hexagonal socket of the'screw head. The plastic cap has slots for receiving the spring-like wire elements. The connecting wire is preferably laterally inserted into the plastic cap. The top of the cap extends over and engages the lateral surface of the screw head.

In accordance with another embodiment of the invention, the metal electrodes are two thin rods intended to clamp together, with the use of two turnbuckles, two parts of a broken bone through which the rods pass. Mounted between the two rods is an electrically insulating body, electrically insulating the two rods from each other. At least one end of each rod is constructed so as to form a receiving element.

The insulating body which electrically insulates the two rods can be in the form of a tube of insulating material which is placed over portions of either one or both of the rods. Alternatively, it is possible to provide the insulating material around a portion of the rods by placing an insert in the openings in' the turnbuckle through which the rods pass or by constructing portions of the turnbuckle itself with insulating material.

The locking element of the corresponding connecting wire can include a plurality of spring biased balls which lockably engage a groove in the rod. Alternatively, the connecting wires can be connected to the rods by utilizing spring clamps as the locking elements,

which clamps are clamped onto the rods.

In all of the embodiments according to the present invention, the locking element has a resilient portion so that the locking element snaps into or onto the corresponding receiving element. Due to the presence of this resilient portion of the locking element, it is also possible to subsequently remove the locking element from the receiving element so as to disconnect the connecting wire from the corresponding electrode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional perspective view of one embodiment of a device for aiding in the formation of bone material according to the present invention with bone screws connected to the fragments of a fractured bone for holding the fragments together.

FIG. 2 is a view of the underside of the locking element associated with the connecting wire for connecting the connecting wire to the corresponding bone screw, in accordance with the device shown in FIG. 1.

FIG. 3 is a cross-sectional side view of the locking element shown in FIG. 2.

FIG. 4 is a partial cross-sectional perspective view of a bone screw with a recess in its head for receiving the locking element shown in FIGS. 2 and 3.

FIG. 4a is a view similar to that of FIG. 4 of a modified embodiment of the device of FIG. 4.

FIG. 5 is a partial cross-sectional perspective view of another embodiment of the device for aiding in the formation of bone material according to the present invention with rods inserted through the fractured bone which rods are interconnected for holding the fragments of the fractured bone together.

FIG. 6a is a partial cross-sectional perspective view similar to that of FIG. 5 of a modified embodiment of the device of FIG. 5.

FIG. 6b is a cross-sectional view showing the connection between one of the locking elements of FIG. 6a and the corresponding rod.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The subject matter of my copending application Ser. No. 26,809, filed Apr. 9, 1970, is incorporated by reference herein to provide a clearer understanding of the present invention.

In FIG. 1, a fractured bone 10 is shown with its fragments reconnected by a plurality of bone screws 12. A pick-up or receiving, coil 16 can be placed into a magnetic field so that an A.C. signal is induced within the coil, which then effectively acts as an A.C. signal source, as described in my above-mentioned prior application. The coil 16 is connected to the bone screws 12 by connecting wires 14 and 15. This connection between the connecting wires and the bone screws will be further described below with reference to FIGS. 2 to 4. The receiving coil 16 is preferably a rod-like ferrite core, on which is applied a singlelayer or multilayer winding, with one end of the winding being connected to the connecting wires 14 and the other end being connected to the connecting wire 15.

In one embodiment of the present invention, details of which are shown in FIGS. 2 to 4, a locking element 18 is mounted on the end of each of the insulated connecting wires, for example the connecting wire 15. The locking element 18 includes a mushroom-shaped part 20 of polytetrafluoroethylene (P.T.F.E.) so that the locking element has a cap-like shape. The connecting wire is radially inserted into part from the side through a kinking protector 22. The connecting wire then passes along the longitudinal axis of the shank of part 20 to three spring wires 24, which are connected together at the center and lead at an angular spacing of 120 along the outside of the shank to the top of part 20. The peripheral surface of the shank is widened at one portion near, or at, the end and the spring wires have corresponding convexities in the location of the widened portion.

The locking element 18 fits into a complementary receiving element formed in the head of the bone screw 12, as shown in FIG. 4. In this embodiment, the bone screw has a known hexagonal socket head, into which a hexagonal spanner can be inserted for both screwing the bone screw into the bone and loosening the screw. The hexagonal socket 25 in the screw head is provided at the rear with a widened portion 26, in which the shank end with the convexed parts of the spring wires 24 can be locked. The top of the part 20 has a crescentshaped cross section so that when it engages the screw head, it extends over the lateral surface and sides of the head.

The locking element 18 can be readily mounted on the screw head even under difficult conditions, for example in a very confined field of operation, and ensures both a secure mechanical seating (and hence also a secure attachment of the receiver coil 16), as well as a satisfactory electrical connection between the connecting wire and the bone screw serving as the electrode.

As another embodiment for the locking element to be connected to a screw head, it is also possible to use a beaker-shaped cap which externally extends over the screw head and locks behind the screw head.

It happens rather frequently that fractures do not heal properly or heal undesirably slow when fixed are fixed by a conventional splint plate attached to the portions of the broken bone by conventional bone screws. This situation can be advantageously dealt with by a modified embodiment of the present invention, which is similar to the embodiment described with reference to FIGS. 1 to 4 with the exception that the bone screws 12 are provided with an electrically insulating coating 28 (e.g. of polytetrafluorethylene) as shown in FIG. 4a. The coating 28 covers a portion of the screw head and an adjacent portion of the shank. To cope with the above mentioned case, the physician replaces two conventional bone screws on opposite sides of the fracture by bone screws 12 having an insulating coating 28, implants the pick-up coil 16 and conncects, the terminals thereof to the screws which are insulated from the splint plate and thus from each other by the insulating coatings.

In accordance with another embodiment of the present invention, two bone parts and 10b of a broken bone can be interconnected with the assistance of two thin but relatively strong metal rods 30, known as Kirschner wires, as shown in FIG. 5. The metal rods 30 are pointed at one end to facilitate their being pushed through the bone and are drawn together in the applied condition by two tumbuckles 32 and 33, whereby the matching ends of the bone parts 10a and 10b are fixed and pressed against each other.

The connecting wires 14 of the A.C. signal source are connected to the metal rods 30, which act as electrodes, via locking elements 34, of which only one is shown in FIG. 5. A locking element 34 is attached to each of the connecting wires 14, which lead to an A.C. source, not shown, such as, for example, a receiving coil, as described with reference to FIG. 1, or an A.C. generator. The parts of the metal rods 30, projecting from the bone, where they pass through the soft tissue 36 surrounding the bone, are surrounded by thin insu- .lating tubes 38 which may consist of thin P.T.E.F.

shrunk-on tubing, and prevent the voltages applied to the metal rods from being short-circuited by the relatively well-conducting soft tissue.

The insulation which is necessary between the two metal rods 30 serving as electrodes in the application of electric currents may be provided either by the insulating tubes 38 or by suitable construction of the turnbuckles 32, 33, which may consist entirely or partly of insulating material, such as, for example, glass-fiber reinforced plastic. In either situation, however, it is preferable to have at least one eye 40 of each turnbuckle include an insulating O-ring 42 of a resilient material such as, for example, rubber, positioned adjacent to the opening through which the rod passes. The O-ring 42 can be compressed by the insertion of a bored clamping screw 43 and when compressed, the ring yields radially inward so that it is finally pressed firmly against the metal rod 30. In this way, a firm mechanical hold of the turnbuckle on the metal rod is ensured, as well as proper electrical insulation between the turnbuckle eye, which has a relatively wide bore, and the metal rod passing through it.

The end of each metal rod 30 remote from the point is constructed so as to form a receiving element adapted to receive the locking element 34. In the embodiment shown in FIG. 5, each metal rod is provided with a machined annular groove 44, in which the corresponding locking element 34 can be locked. The locking element 34 includes radially slidable and lockable balls 31 which can be locked in the annular groove 44.

As shown in FIG, 6a, the connecting wires 14 and 15 from a receiving coil 16, serving as A.C. source, can be clamped to the rods 30, with the use of, for example, U-shaped metal spring clamps 45. The clamps 45 are electrically connected to the ends of the winding of the receiving coil and are clamped onto noninsulated sections of the metal rods 30. The clamp 45 which is connected to the connecting wire 15 is shown in FIGv 6a, on an enlarged scale, clamped onto the rod 30. In this way, the receiving coil 16 is mechanically attached to the metal rods 30 and is also electrically connected to them.

The use of bone screws, for example of a known physiologically well compatible CoCr-Mo alloy, as

electrodes, where alternating electrical potentials of less than one volt in a given frequency range greater than 1 Hertz (i.e. 1c/,) are applied, is possible without the risk of metallosis (i.e. electrolytic solution of living tissue).

The device shown in FIGS. 1 to 4 is especially advantageous in providing a simple mariner for repositioning of the fractured bones, which can be utilized in many cases of bone fracture. This device utilizes bone screws without any supporting plate for repositioning the fractured bone while at the same time providing for electrical stimulation of bone growth. With the use of bone screws without a plate the danger of infection is reduced. In the absence of a sufficient covering of soft tissue around the bone, for example in the case of tibia fractures in children and elderly persons, it frequently happens that the plate cannot be implanted. Repositioning the bone parts with screws without the use of a plate results in long periods of lying in bed because of the lack of stability. These periods can be significantly shortened, for example, by up to one half, by the use of electrostimulation of the bone growth.

Since the device shown in FIGS. 1 to 4 is to be implanted, all of the parts that will come into contact with tissue or bone are made of physiologically compatible, sterilizable materials. If the receiving coil 16, such as shown in FIGS. 1 and 6a, is used as the current source, a low-frequency alternating current (with the frequency preferably below Hertz, with the signals having gradually rising and falling flanks) is then induced by an external magnet field, as described for example in the abovementioned German Pat. No. 1,918,299 of German Offenlegungschrift (laid-open specification) No. 2,1 16,869.

It wil be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

1. In an implantable device for promoting the formation of bone material in the region of the bone structure of a living being by the application of an AC. signal, the device including at least two metal bone screws capable of being inserted into the bone structure and a pick-up coil having at least two connecting wires, each of which is to be electrically connected to a corresponding one of the metal bone screws, the improvement comprising: a plurality of first locking means each connected to a respective one of said connecting wires; and receiving means provided by each of said bone screws for receiving said locking means of said corresponding connecting wire so that each said connecting wire is connected in an interlocking relationship to said corresponding bone screw.

2. In a device for promoting the formation of bone material in the region of the bone structure of a living being by the application of an AC. signal, the device including at least two metal electrodes capable of being inserted into the bone structure and an AC. signal source having at least two flexible connecting wires, each of which is to be electrically connected to a corresponding one of the metal electrodes, the improvement comprising: a plurality of first locking means each connected to a respective one of said connecting wires and receiving means disposed on each of said metal electrodes for receiving said locking means of said corresponding connecting wire so that each said connecting wire is connected in an interlocking relationship to said corresponding metal electrode, wherein each said electrode includes a bone screw, whose head has a recess therein forming said receiving means and said locking means includes a cap-like connecting element formed so as to securely fit in said recess in said screw head of said corresponding electrode.

3. A device as defined in claim 2, wherein said recess in said screw head is a hexagonal socket, which internally has a widened portion, and said cap-like connecting element is substantially mushroom-shaped with a widened portion along the peripheral surface of its shank, corresponding to the widened portion of said hexagonal socket, further comprises: connecting electrodes electrically connected to said connecting wires and disposed on the axial surface of said connecting element such that when said connecting element is inserted into said hexagonal socket said connecting electrodes are clamped therebetween.

4. A device as defined in claim 3, wherein said connecting wire is connected to said connecting element so 7 8 as to be perpendicularly disposed with respect to the ing wires can be subsequently disconnected from said longitudinal axis of said connecting element. electrodes.

5. A device as defined in claim 1, wherein said lock- 6. A device as defined in claim 2 wherein said signal ing means includes resilient means which releasably insource comprises a pick-up coil. terlocks with said receiving means so that said connect- 5 

1. In an implantable device for promoting the formation of bone material in the region of the bone structure of a living being by the application of an A.C. signal, the device including at least two metal bone screws capable of being inserted into the bone structure and a pick-up coil having at least two connecting wires, each of which is to be electrically connected to a corresponding one of the metal bone screws, the improvement comprising: a plurality of first locking means each connected to a respective one of said connecting wires; and receiving means provided by each of said bone screws for receiving said locking means of said corresponding connecting wire so that each said connecting wire is connected in an interlocking relationship to said corresponding bone screw.
 2. In a device for promoting the formation of bone material in the region of the bone structure of a living being by the application of an A.C. signal, the device including at least two metal electrodes capable of being inserted into the bone structure and an A.C. signal source having at least two flexible connecting wires, each of which is to be electrically connected to a corresponding one of the metal electrodes, the improvement comprising: a plurality of first locking means each connected to a respective one of said connecting wires and receiving means disposed on each of said metal electrodes for receiving said locking means of said corresponding connecting wire so that each said connecting wire is connected in an interlocking relationship to said corresponding metal electrode, wherein each said electrode includes a bone screw, whose head has a recess therein forming said receiving means and said locking means includes a cap-like connecting element formed so as to securely fit in said recess in said screw head of said corresponding electrode.
 3. A device as defined in claim 2, wherein said recess in said screw head is a hexagonal socket, which internally has a widened portion, and said cap-like connecting element is substantially mushroom-shaped with a widened portion along the peripheral surface of its shank, corresponding to the widened portion of said hexagonal socket, further comprises: connecting electrodes electrically connected to said connecting wires and disposed on the axial surface of said connecting element such that when said connecting element is inserted into said hexagonal socket said connecting electrodes are clamped therebetween.
 4. A device as defined in claim 3, wherein said connecting wire is connected to said connecting element so as to be perpendicularly disposed with respect to the longitudinal axis of said connecting element.
 5. A device as defined in claim 1, wherein said locking means includes resilient means which releasably interlocks with said receiving means so that said connecting wires can be subsequently disconnected from said electrodes.
 6. A device as defined in claim 2 wherein said signal source comprises a pick-up coil. 